1. Field of the Invention
The present invention generally pertains to filter assemblies for treating contaminated air passing therethrough. More particularly, the invention relates to a filter assembly for removing toxic aerosols from the air that is designed to minimize the formation of voids and the occurrence of bridging in a filter media in the filter assembly, even over extended periods of time. The filter assembly is also provided with a detection mechanism which enables an operator to determine the extent to which the filter has become defective.
2. Discussion of the Prior Art
Filter systems, such as charcoal filters and paper filters, for treating air have a wide variety of applications which are well known in the art. Such filters are commonly used as breathing apparatus for fire fighters, miners, and soldiers in the field. Additionally, these filters are often used in the military in such things as vehicles, ships, and the like, in the event that troops are exposed to toxic agents or poisonous gases. A particular military concern is the exposure of crew members of a naval ship to toxic gases, for example, generated by rockets flying nearby. A rocket employed for germ warfare could release anthrax or other deadly materials. These would pose serious health dangers to the occupants of a ship.
Nuclear, biological, and chemical filtration devices, commonly referred to as xe2x80x9cNBCxe2x80x9d devices, are currently available to the Government and other consumers to treat contaminated air in environments described above as well as other environments. NBC devices generally employ a filtration cartridge which filters air that enters the subject environment. A conventional filtration cartridge comprises a cylindrical inner ring-like wall surrounded by a cylindrical outer wall. The inner and outer walls are usually formed from a perforated metal material and are co-axially disposed to define an annular filtering space therebetween. A filtering media occupies the space defined between the inner and outer cylindrical walls. The filtering media is usually a granulated charcoal material but could be any other appropriate absorbent material. Axial end walls are disposed at both ends of the cartridge. In operation, air is drawn radially into the cartridge and filtered by the absorbent media. The airflow can be either radially inward or radially outward through the filter media.
During storage and in use, the filter cartridge is subjected to vibration and may possibly even be dropped. If continuous pressure is not kept on the filter media, the particles will begin to abrade one another. As the particles grind themselves into dust, the apparent density or packaging density of the filter media increases. This means the amount of carbon originally placed in the filter now occupies a smaller space. This process is self-supporting because as voids are formed there is room for additional abrading. If voids form in the granulated filter media and these are not filled, bridging occurs. Toxic gases such as nerve gases, anthrax, or other aerosols will pass through the voids and out the perforated screen walls of the filter cartridge. Obviously, this creates a hazardous condition. As one can appreciate, the elimination of voids and bridging is critical to the safety of military personnel. An important feature of the known filter system is the provision of compression pads located at one or both ends of the filter cartridge. The compression pads operate to exert pressure (at approximately 5,000 psig) in the longitudinal direction on the granulated filtering medium compacting the absorbing particles. As pressure is increased, the potential for voids and bridging is diminished.
Currently, the compression pads in conventional filtering devices suffer from at least one significant shortcoming. The pads are usually made from a rubber material. However, the rubber does not have sufficient memory after a period of two or three days to maintain a constant compression force on the granulated filter material. Therefore, after a certain period of time, rubber compression pads cannot be relied upon to exert a specific force. As such, the known filter devices are prone to suffer from voids and bridging resulting in the dangerous conditions previously discussed.
Another shortcoming of present filter cartridges is the inability to perform a non-destructive evaluation prior to placing the unit into service. It is not uncommon for filter assemblies to sit in storage for long periods of time. During their lifetime, they are often dropped during transport or are subject to vibration, both of which may cause voids or defects in the filter assembly. Currently, a representative sample of filters is subjected to destructive testing prior to acceptance. Representative testing is not capable of testing each individual filter assembly. Moreover, after this testing, no further evaluation of the filter is made during the filter""s lifetime, even after potentially damaging impacts or severe vibrations.
Accordingly, it has been considered desirable to develop a new and improved filtering device capable of applying a continuous and specific compression force on the filtering medium, thereby minimizing the formation of voids and the occurrence of bridging. Also, a filter assembly capable of being evaluated for voids and defects in a non-destructive manner would be of benefit to both a manufacturer and an end user.
In accordance with the present invention, a new and improved filtering device with a non-destructive testing device is provided.
More particularly, in accordance with one aspect of the present invention, a filter assembly with a non-destructive testing device includes a substantially toroidal filter cartridge having a first outer cylindrical wall spaced from and surrounding a second inner cylindrical wall. The outer and inner walls define an annular space therebetween. A filtering media is disposed within the annular space for removing contaminants from a medium passing through the filter cartridge. A first biasing assembly is located at a first axial end of the filter cartridge for exerting a constant and specific compression force on the filtering media. A sensing mechanism to be applied to the filter cartridge detects changes in the biasing assembly which result from the formation of defects in the filtering media.
In accordance with another aspect of the present invention, a filter assembly includes a substantially toroidal filter cartridge having a first outer cylindrical wall spaced from and surrounding a second inner cylindrical wall. The outer and inner cylindrical walls define an annular space therebetween. A filtering media is disposed within the annular space for removing contaminants from a medium passing through the filter cartridge. A first pre-compressed biasing assembly is disposed at a first axial end of the filter cartridge. The first biasing assembly has at least a portion configured to unload and spread in a direction other than an axial direction of the filter cartridge when a force exerted by the filtering media exceeds a loading of the biasing member.
A preferred method of non-destructively testing a filter assembly to verify continuity of a filtering media disposed within a filter cartridge of the filter assembly includes pre-compressing a biasing member to a predetermined load. The biasing member is then positioned adjacent a first axial end of the filter cartridge so that the biasing member applies a continuous and constant force on the filtering media. The spread and unloading of the biasing member is then measured with a Hall Effect sensing mechanism.
One aspect of the present invention is the provision of a new and improved filter cartridge for treating contaminated fluids.
Another aspect of the present invention is the provision of a filter cartridge employing a granular filter media in which voids and bridging of the granular media is minimized.
Still another aspect of the present invention is the provision of a filter cartridge employing a spring assembly capable of applying a specific compression force to a filtering medium over an extended period of time.
Yet another aspect of the present invention is the provision of an annular filter cartridge employing a granular filter media and at least one spring member which exerts an axial compression force on the granular filter media.
A further aspect of the present invention is the provision of a non-destructive testing means for a filter cartridge to determine whether voids or defects have formed in the filter media held in the filter cartridge.
A still further aspect of the present invention is the provision of a means for determining the remaining compressive force in each spring assembly of a filter cartridge without destroying the filter cartridge. This is done through the use of a sensing mechanism which can detect the location and spread of a spring assembly within the walls of the filter cartridge. The values obtained with the measuring device could be compared to the values measured when the filter cartridge was originally constructed, and a determination made as to the condition of the filter cartridge.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification.